The invention concerns a process and a device for the placement and fixing of sheets of filaments, in the course of the production of scrims, which are implemented in a connecting station into a flat structure having, among other elements, the filament sheets.
The connecting station can, for example, be a warp knitting machine or a calender in which the previously placed and fixed filaments can be knitted and/or connected with one another in such a way that a flat scrim thereby arises. The filaments serve, on one hand, as so-called weft yarns in the production of scrims and, on the other hand, are increasingly used for purposeful reinforcement of the scrim to be produced, depending on their material. Placing these types of weft yarns continuously and in a meander shape by means of a weft carriage between two rows of needles moving forward via conveyor bands is known, with the yarns being hung on the rows of conveyor needles of a conveyor device. Lateral fixing of the weft yarns placed in this way is only required until the individual yarns are knitted or otherwise connected with one another in the connecting station. Subsequently, laterally projecting weft yarns can be cut off. These cut-off parts of the yarns are to be disposed of as filament waste of the production process.
Increasingly, these types of scrims for reinforcement are produced with high-value yarns and/or filaments, such as glass or carbon fibers. In this regard, the known methods for fixing and placement of the yarns have the disadvantage that on one hand, cost-intensive waste arises due to the cut-off remainders of high-value and thereby expensive yarns projecting at the edge of the scrim and, on the other hand, problems hereby arise because distortions and irregularities in the yarn guiding occur due to the twisting of the yarns or yarn sheets at the reversal points and/or around the conveyor needles, which leads to the placed and fixed yarns not forming a smooth plane. In the subsequent knitting process in a connecting station, this regularly leads to knitted materials of poor quality. The latter problem particularly arises when yarns are collected into so-called yarn sheets, because these cannot, and/or not without further means, be placed smoothly as flat bands around the rows of conveyor needles fixed laterally on the conveyor chains. The problem particularly occurs when so-called xe2x80x9cheavy tows,xe2x80x9d i.e., filament sheets with a high number of filaments of a magnitude of approximately 104, made of, for example, materials such as carbon or glass, are to be used for the production of scrims. Placement of these types of materials is, any case, only possible in very restricted cases (cf. Kettenwirkpraxis [Practical Warp Knitting] 2/96 p. 7).
The object of the present invention is to provide a process and a device for the placement and fixing of filament and/or yarn sheets, for the production of flat scrims, having an essentially uniform filament density, and to allow the use of filament sheets with various materials and to improve their secure fixing until connecting in a connecting station, particularly in a knitting station.
This object is achieved by a process with the features according to claim 1 and/or by a device with the features according to claim 11. Advantageous embodiments and further developments of the invention are objects of the respective sub-claims.
According to the process for placement and fixing of a filament sheet according to the invention, the filament sheet is placed as a filament sheet section between two conveyor units supplying a connecting station, with the filament sheet sections each being fixed onto the conveyor unit at each of their end regions with a fixing element and the interval of the fixing elements of one single filament sheet section relative to the conveyor unit being selected in such a way that, in their fixed condition, the filament sheet sections are positioned essentially flat between the conveyor units, at least immediately before entering the connecting station. Because the filament sheet is placed and fixed on the conveyor unit as separate filament sheet sections, each with fixing elements at their ends, the filament sheet is prevented from twisting, as in the meander-shaped placement, and thereby being placed out of its plane and thus irregularly. Rather, it is ensured with high reliability that the filament sheet, i.e., each individual filament of this filament sheet, is placed and fixed in a preset plane. In this way, not only is the quality of the scrim to be produced greatly improved, it is now also possible according to the invention to use relatively wide or stiff filament sheets or yarn sheets for processing into flat high-performance scrims. Furthermore, the resulting residues arising laterally on the scrim, which must be cut off and disposed of as waste, are reduced. Rather, the filament sheet sections can be exactly dimensioned in such a way that the fixing elements have exactly enough hold on the ends of the filament sheet sections to hold the filament sheet sections securely even under light pretension. The productivity of the production of scrims is thereby significantly increased, with the production able to be performed in less time and at lower cost. Because a weft carriage no longer places individual yarns, but rather wide filament sheet sections with an entire sheet of filaments, the placement speed can be increased. In addition, the variability in the placement of filament sheets can be increased with the process according to the invention, for example by also making multiaxial and multilayer placement of yarn sheets possible.
Although the filament sheets are placed without being twisted, good fixing by the lateral fixing elements is ensured at all times. The use of band-shaped filament sheet sections also has the advantage that, because they are a significantly less expensive starting material than individual yarns, the overall cost of the scrim to be produced can also be reduced.
According to an advantageous embodiment of the invention, the fixing elements are attached at a slant to the filament sheet section, i.e., to the lengthwise direction of the filament sheet section, at a selectable angle for diagonal placement of the filament sheet sections. This has the advantage that the strength of the scrim to be produced can be increased further, for example through superposition of straight and diagonally running filament sheet sections. The tensile strength of this type of material can thus be purposely adjusted according to the application in every direction. Because each filament sheet section is provided with two end fixing elements, they can be provided at any angle, i.e., of course also at any distance to one another, depending on the diagonal angle selected, and correspondingly be placed on the conveyor unit, with a reliable, and nonetheless very exact, placement, located in one single plane, of the filament sheets being ensured. The yarn sheets and/or yarn bands can thus not only be simply placed on top of one another, but can also be positioned and fixed unidirectionally, biaxially, or multiaxially in the placement range.
According to a further advantageous embodiment of the invention, the fixing elements of a filament sheet section are hung on holding needles of a conveyor unit. In this way, the individual filament sheet sections are securely fixed between the holding needles in a very simple way. Nonetheless, they can be easily hung as desired, even on top one another, and thereby fixed. For filament sheet sections which are laid on top one another, it is advantageous for the holding needles to have a radius of curvature, so that the individual filament sheet sections have a uniform tension over the working width due to the greater thickness of the fixing elements at the end regions. Continuous, uniform placement and fixing is possible in this way, independent of the individual filament sheet section. The hanging or also removal of filament sheet sections can be performed rapidly and with simple means.
According to a further advantageous embodiment of the invention, the fixing elements are produced by embedding the end regions of the filament sheet sections, preferably in a rapidly hardening plastic or a metal and/or a eutectic metal alloy. This has the advantage of great practicability, because the fixing element can be easily connected with the filament sheet section, independent of the material. In addition, these fixing element sheet sections are extremely economical and also can be relatively rapidly produced in the connecting station, depending on the processing speed. This type of fixing element also has the advantage that, after solidification, it is extremely solid and thereby provides the filament sheet section a secure hold on all of the filaments connected with it, and nonetheless has favorable properties in regard to weight and material costs.
According to a further advantageous embodiment of the invention, the fixing elements are produced by gluing of the end regions of the filament sheet sections. This has the advantage that fixing elements can be produced, even at very high speeds, with rapidly hardening materials and, furthermore, with any desired fixing element parts in the material. The placement and fixing speed can thus be further increased.
According to a further advantageous embodiment of the invention, the process has the following steps:
Attachment of a first fixing element 2xe2x80x2 to the filament sheet;
Gripping of the first fixing element 2xe2x80x2 and movement of the fixing element 2xe2x80x2 by a preset distance b;
The application of a second fixing element 3xe2x80x2 to form the first filament sheet section and preferably also a first fixing element for the subsequent filament sheet section;
Cutting off the first filament sheet section and hooking or pressing the fixing element into the respective holding needles or, conversely, first hooking or pressing and then cutting off the filament sheet section.
The individual process steps described can hereby be performed continuously and synchronously for each following filament sheet section, so that no delay of the actual connecting procedure in the connecting station occurs due to the production of the filament sheet sections provided with the fixing elements. It is, however, also possible to implement the second fixing element of the first filament sheet section and the first fixing element of the subsequent filament sheet section in one piece and then to cut them apart. With a few very simple steps, very high-quality scrim materials can thus be produced. Through use of reinforcement filament sheets, which is purposeful in regard to material and placement, the variability in the production of high-performance knitted scrims is significantly increased.
According to a further advantageous embodiment of the invention, a predefined filament sheet tension is applied to the individual filament sheet section in the process step d of the present invention between cutting and hooking and/or pressing. In this way, it is ensured that each filament sheet, and thereby also each filament in a filament sheet, is connected to the scrim in the connecting station with a uniform pretension, so that the elements are evened out as much as possible before possibly marked undulations and no distortions or irregularities arise in the filament density and thereby in the stretching and tensile properties of the scrim due to irregularly tensioned filament sheet sections.
According to a further advantageous embodiment of the invention, the filament sheet sections are produced in coordination with the supply speed of the rows of needles. In this way it is ensured that the placement and fixing steps can be optimally adjusted to the operating speed of the following connecting station. Therefore there is no delay or overtaking of, on one hand, the preparation steps of placement and fixing and, on the other hand, of the connecting of the scrim having the filament sheets as a part.
According to a further advantageous embodiment of the invention, several filament sheet sections are placed and fixed on top of one another. In this way, on one hand, the strength of the scrim to be produced can be increased further, and, on the other hand, the thickness of the scrim can be controlled.
The device for placement and fixing of the filament sheets implemented as a closed surface according to a first exemplary embodiment of the invention has parallel conveyor chains which supply continuously, a placement unit for laying the filament sheet, and a holding unit for at least temporary fixing of the placed filament sheets, with the sheets being supplied to a connecting station for production of flat scrims and with a unit for the production of prefabricated filament sheet sections being provided. This unit produces filament sheet sections which are provided at a preset interval with fixing elements and which can be attached to the supplying conveyor chains in such a way that, at least at the connecting station, the filament sheet sections are held in such a way that they are implemented there as an essentially flat surface. Thus, the individual filament sheet sections provided with fixing elements can not only be produced very easily in accompaniment with the process, but they can also be placed and fixed, without complicated holding or placement mechanisms, in the holding devices provided on the conveyor chains. The interval of the conveyor chains of the device and interval of the fixing elements are adjusted to one another in such a way that it is, in fact, not necessary for the filament sheet to be tensioned between the conveyor chains at the moment of placement, but that, at latest shortly before the connecting station, all of the filament sheet sections placed in the device are positioned uniformly and thus essentially in one plane, i.e., are fixed with pretension.
According to advantageous embodiment of the invention, the holding unit has a row of guide needles and a row of holding needles into which the fixing elements can each be hooked and/or pressed. For example, in a filament sheet with individual filaments, which are positioned very close to one another, the guide needles can be implemented as so fine that channels hardly arise in the filament sheet. In addition, it is hereby ensured that the filament sheet sections are held securely as they enter the connecting station, they are fixed in their position, and they have a uniform filament density. The device thus has a very simple construction and functions with a few breakdowns and little need for maintenance.
According to a further embodiment of the invention in this regard, the placement unit has a gripper unit, which can be moved and lowered, having at least one presser, one gripper, and one cutting knife. The gripper unit can thereby be moved transversely or diagonally to the supply direction of the conveyor unit as desired, so that filament sheet sections produced, i.e., provided with fixing elements, laterally to the placement direction can be gripped by the gripper and, after traveling over the placement device into the corresponding opposite row of holding needles, can be pressed by one or more pressers into the row of needles. The cutting knife serves for cutting off individual filament sheet sections from the endless roll of filament, with this preferably occurring after hanging on both ends, i.e., fixing of a filament sheet section, and preferably at the rear end in the direction of placement, before the following section can be picked up by the gripper of the gripper unit.
According to a further advantageous embodiment of the invention, the holding needles of the holding device are of a length such that several fixing elements, and thereby several filament sheet sections, can be hooked into them on top of one another. Because the holding needles are positioned below the row of guide needles, the holding needles can be implemented sufficiently long for this purpose without interfering with other functions of the device. In this way, high-strength scrims, i.e., those having several layers of filament sheet sections on top of one another, can also be produced.
According to a further advantageous embodiment of the invention, the interval of the holding needles positioned on the respective conveyor chains increases in the direction of movement of the conveyor chains to pretension the filament sheet sections. This has the advantage that the interval between the holding needles can be reduced in such a way that, at the placement position at which the individual filament sheet sections are placed, the hanging by means of the gripper unit is made significantly easier and nonetheless, at least at the connecting station, the filament sheet sections are uniformly fixed and tensioned and can also not pop out of the holding device under any circumstances.
According to a further advantageous embodiment of the invention, the holding unit on the conveyor chains only has one row of holding needles. In this case, the holding needles assume the double function of transportation and/or guiding of the filament sheet sections and, simultaneously, fixing and holding. Because the holding needles are positioned below the uppermost edge of the conveyor chains, the filament sheet sections are guided via this edge and are thereby uniformly supplied to the connecting station to maintain an essentially constant filament density without the formation of channels. The device has a constructively simple design, has fewer single parts, and nonetheless ensures easy placement and fixing, even of so-called xe2x80x9cheavy towsxe2x80x9d for the production of high-performance scrims.
According to a further advantageous embodiment of the invention, a device for the production of the filament sheet sections is provided which allows fusing, embedding, and/or gluing, and/or freezing of the fixing elements with the filament sheet sections. While fusing has the advantage of an extremely solid bond of the fixing elements with the filaments, rapid connecting of the fixing elements with the filament sheets can be achieved, independent of the material, with gluing. Embedding and/or casting in has the advantage that the filament sheet does not fuse with the fixing elements and thus can be removed again by heating if necessary. Freezing of the filament sheet sections to fixing elements at the end regions not only has ecological advantages, but is also extremely economical and, nonetheless, ensures secure fixing, i.e., attachment, of the fixing elements to the filament sheet sections. In addition, lateral remainders can be supplied to a recycling center without contaminants after thawing.
According to a further advantageous embodiment of the invention, an angle, at which the fixing elements can be fixed to the filament sheet section at a slant, can be set on the device. In this way, individual filament sheet sections can be placed not only at 90xc2x0, but also diagonally at any desired angle, with the filament sheet sections nonetheless able to be inserted and fixed securely.
According to an embodiment of the invention related to this, a control unit is provided for control of the placement unit and the unit for production of the filament sheet sections. The control unit can hereby be used, on one hand, for control of the placement geometry, i.e., the axial alignment, and, on the other hand, for the control of the placement and fixing speeds of the device, which are adjusted to the production process of the scrim.